ci: ratchet the bundle budget and scan builds for credentials (FH-3.3, FH-3.5)

Bundle budget was warning-only: initial warning 700 kB, error 1.8 MB.
Measured today the initial bundle is 1.55 MB raw / 324.58 kB transfer -
up from the 1.15 MB measured on 11 August, so it had been growing with
nothing to stop it.

Lowers maximumError to 1.6 MB. That is a ratchet, not a target: just
above today's size so the bundle cannot grow, with the 700 kB warning
left in place as the goal. Lower it each time the number comes down.

Adds scripts/ci/scan-bundle.sh (npm run scan:bundle), run in CI after
the build. Seven patterns: both provider auth headers, the partner ID
shape, client_secret, private key blocks, AWS keys, Telegram bot
tokens. The legacy payment code that put credentials in the browser is
already deleted; this is what stops it coming back. Verified in both
directions - clean against the real dist, exit 1 against a planted
credential.

Measurement also corrected two assumptions recorded in the harvest
TODO: admin and editor code is already lazy-loaded, so the initial
bundle is main alone rather than a deployable-split problem; and mock
gateway fixtures do reach production chunks, which is now filed as
FH-E.6 with the cause identified.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

.github/workflows/architecture-governance.yml

@@ -40,9 +40,19 @@ jobs:
           CHROME_BIN: ${{ steps.setup-chrome.outputs.chrome-path }}
         run: npm run test:coverage
 
+      # The production build is what enforces the bundle budget. The initial
+      # bundle sits at ~1.55 MB raw against a 700 kB target, so the error
+      # threshold is a ratchet, not the goal: it is set just above today's
+      # size so the bundle cannot grow while we work it back down. Lower the
+      # ratchet in angular.json every time it comes down.
       - name: Build
         run: npm run build
 
+      # Stops payment credentials returning to the browser bundle. See
+      # scripts/ci/scan-bundle.sh for what it looks for and why.
+      - name: Scan bundle for credentials
+        run: npm run scan:bundle
+
       - name: E2E
         run: |
           npx playwright install --with-deps chromium